International Review of Hydrobiology最新文献

The construction of reservoirs impacts upon freshwater ecosystems, since it changes the hydrodynamics of the entire system upstream and downstream of the dam due to flow control and changes in environmental conditions. We analyzed the temporal variation in the abundance of exogenous testate amoebae related to the suspended inorganic material in Neotropical floodplain lakes, downstream of a series of dams. Sampling was carried out between 2000 and 2012 in six lakes in the upper Paraná River floodplain. The temporal variation in the abundance of the testate amoeba community was analyzed using the Threshold Indicator Taxa Analysis. Cucurbitella crateriformis, Protocucurbitella coroniformes, and C dentata f. quinquilobata had reduced population growth in higher concentrations of suspended inorganic material. On the other hand, Difflugia lobostoma, Centropyxis ecornis, and Difflugia pseudogramen populations increased under these conditions. These results showed that an increased flow of water could favor the growth of some populations due to the greater exchange of material between the lakes and the floodplain. The positive or negative responses could show better adaptation of the testate amoeba species to the planktonic environment. Furthermore, these results also highlighted the bioindicator role of these protozoa in aquatic ecosystems.

The spatial distribution of benthic macroinvertebrates along reed transects was studied in lakes with minimal human disturbances to enable a deeper understanding of the functioning of reed macroinvertebrate communities and relations to biotic and abiotic environmental variables. The taxonomic and functional macroinvertebrate community composition significantly differed between outer margin, center, and shore locations. At shore locations, higher proportions of Gastropoda, Hydrachnidia and Coleoptera, mobile swimmers/skaters, predators, and shredders were found. However, outer margin locations were characterized by a higher proportion of sessile filter-feeding Bivalvia and mining Diptera. At the outer margins, also greater contributions of taxa preferring pelal habitats and r-strategists typical for more disturbed environments were observed. An indicator species analysis revealed Asellus aquaticus (Crustacea) and Scirtidae Gen sp. (Coleoptera) as significant indicator taxa for shore locations and Valvata piscinalis (Gastropoda), Tinodes sp. and Orthotrichia sp. (Trichoptera) as significant indicator taxa for outer margin locations. The taxonomic composition of macroinvertebrate communities was significantly related to higher water depth, oxygen content, and pH at outer margin locations. Shore locations were characterized by higher amounts of woody debris, leaf litter, and decaying plant material. In summary, the taxonomic and functional composition of macroinvertebrates varied strongly from shore to outer margin locations and could be related to spatial changes in hydrodynamical and food conditions along the transects.

Gymnotus is the most species rich genus of electric fish in the Neotropical region. Recently, a previously unknown diversity has been found in this genus, motivating a pursuit for new species. In this study, a fragment of the mitochondrial Cytochrome c Oxidase subunit I (COI) gene was used to analyze the diversity of 10 morphospecies of Gymnotus (G. carapo, G. pantanal, G. sylvius, G. ineaquilabiatus, G. pantherinus, G. coropinae, G. jonasi, G. cylindricus, G. chaviro, G. tigre) in two Neotropical river basins (Paraná River and Doce River), in addition to specimens identified as Gymnotus sp. At least 15 OTUs were determined, eight of which belonged to the carapo complex. Our results indicate the existence of at least four Gymnotus species belonging to the carapo clade in the upper Paraná River basin and possibly erroneous previous identifications. Besides that, we identified a possible new species of Gymnotus in the Rio Doce basin. The Generalized Mixed Yule Coalescent (GMYC) and Poisson Tree Processes (PTP) molecular delimitation approaches place other specimens found in the upper Paraná River and Guaíba River (Gymnotus sp.) in well-established groups that should be considered in studies involving the carapo complex.

The goal of this study is to experimentally assess the possible effect of macroinvertebrate predators on the decomposition rate of leaves in a Mediterranean stream and to analyze the pattern of colonization by macroinvertebrates of the litter bags through time. We designed a factorial experiment with three types of litter bags (allowing the entrance of no macroinvertebrates, only small macroinvertebrates and small and large, top-predators, macroinvertebrates). We measured the percentage of ash-free dry mass remaining after 15, 30, and 45 days, as well as the macroinvertebrate community composition of the two types of litter bags where they were allowed to enter. We did not find differences in the ash-free dry mass remaining between the two types that allowed the entrance of macroinvertebrates. The diversity of the community colonizing each type of litter bag was always relatively high and changed significantly with time and, in some cases, with the exclosure treatment studied. These results show the absence of important top-down control of macroinvertebrates and particularly in those involved in the leaf decomposition in the food web of this Mediterranean stream that could have repercussions on the leaf decomposition process.